Allergy and Tissue Metabolism

W. G. Smith

• Publisher: Butterworth-Heinemann
• Year: 2013
• Print ISBN:
  9781483200354
• eBook ISBN:
  9781483225388
• Topic: Biological Sciences
• Subtopic: Evolution
• Index: Biological Sciences

Allergy and Tissue Metabolism covers some of the more important features of the state of knowledge in the relevant areas of allergy and tissue metabolism. This book is composed of nine chapters, and starts with a survey of the link between immune system and allergic diseases. The subsequent chapters deal with the evaluation of anaphylactic shock mechanisms using some animal models and the relationship between eosinophils and anaphylaxis. These topics are followed by discussions on the role of histamine, bradykinin, and serotonin in allergy. A chapter examines the slow reacting substance of anaphylaxis. The final chapters consider the therapeutic management of allergic diseases. This book is of value to allergists, allergologists, immunologists, and researchers and workers in the allied fields.

Chapter I

The immunological basis of allergic disease

Publisher Summary

This chapter discusses the immunological basis of allergic disease. During the period when the body is recovering from certain infectious diseases, it becomes more resistant to the organism responsible for the infection. This increased resistance is known as acquired immunity. Its duration depends upon the nature and severity of the infection. The immunity acquired in this way is associated with the appearance in the blood of substances called antibodies, which have properties enabling them to combine specifically with the infecting organism or a toxin produced by it. Substances that stimulate the formation of antibodies in this way, and react with them specifically, are known as antigens. Conversely, a substance that appears in the blood or body fluids as the result of the parenteral administration of an antigen, and that reacts specifically with that antigen, is called an antibody. It seems quite probable that in all infective disease of long enough duration to allow an immunological response, symptoms due to hypersensitivity to bacterial or viral products are present, superimposed on those because of the direct effects of the infecting organisms themselves.

During the period when the body is recovering from certain infectious diseases it becomes more resistant to the organism responsible for the infection. This increased resistance is known as acquired immunity. Its duration depends upon the nature and severity of the infection; so that it may be weak and transient on the one hand or substantial and lifelong on the other. The immunity acquired in this way is associated with the appearance in the blood of substances called antibodies, which have properties enabling them to combine specifically with the infecting organism or a toxin produced by it. The first clear demonstrations of the formation of antibodies were made during the last ten years of the last century, and soon shown to be examples of a general phenomenon in which a large variety of foreign cells and simpler entities like protein molecules stimulate the production of specific antibodies if they are injected parenterally into the mammalian body. Substances that stimulate the formation of antibodies in this way, and react with them specifically, are known as antigens. Conversely, a substance that appears in the blood or body fluids as the result of the parenteral administration of an antigen, and that reacts specifically with that antigen, is called an antibody.

Early observations showed that when the antigen is a soluble substance such as a foreign protein, its combination with specific antibody contained in an antiserum often led to the formation of a precipitate. The antibodies were then termed precipitins. When the antigen was a constituent of foreign cells, such as erythrocytes from another species of animal, the combination of antigen and antibody caused the cells to agglutinate. The antibody was then called an agglutinin. It is now clear, however, that a single antibody can be involved in either the formation of a precipitate or the agglutination of cells according to the situation of the specific antigen with which it reacts.

Unfortunately, the production of antibodies does not always have beneficial results. It may have the very reverse effect when the body cells experience an antigen for the second time, resulting in severe symptoms and even death. This phenomenon, whereby an immunological response involving combination of antigen and antibody is the cause of reactions which are damaging to cells, is called allergy or hypersensitivity. Hypersensitivity can occur in a large number of conditions, some produced artificially, others occurring naturally, and a number associated with infective disease. The relationship between the hypersensitive state and the production of antibodies is in some cases quite clear, but in others, antibodies have not as yet been detected and the immunological basis for the conditions can only be inferred indirectly. It seems quite probable that in all infective disease of long enough duration to allow an immunological response, symptoms due to hypersensitivity to bacterial or viral products are present, superimposed on those due to the direct effects of the infecting organisms themselves.

The relationship between hypersensitivity and antibody production can be most clearly demonstrated where the hypersensitive state is produced artificially; a condition known as anaphylaxis. This term is compounded from the Greek and suggests that guarding (phylaxis) is reversed (ana). It was first used by the French physiologist Richet¹“While endeavouring to determine the toxic dose (of extracts of sea anemone), we soon discovered that some days must elapse before fixing it; for several dogs did not die until the fourth or fifth day after administration or even later. We kept those that had been given insufficient to kill, in order to carry out a second investigation upon these when they had recovered. At this point an unforseen event occurred. The dogs which had recovered were intensely sensitive and died a few minutes after the administration of small doses. The most typical experiment, that in which the result was indisputable, was carried out on a particularly healthy dog. It was given at first 0·1 ml. of the glycerin extract without becoming ill; twenty two days later, as it was in perfect health, I gave a second injection of the same amount. In a few seconds it was extremely ill; breathing became distressful and panting; it could scarcely drag itself along, lay on its side, was seized with diarrhœa, vomited blood and died in twenty five minutes.”

A somewhat similar observation had been made in England at about the same time by Theobald Smith in guinea pigs used for the assay of diphtheria antitoxin. Animals injected with neutral mixtures of toxin and antitoxic serum, and which therefore survived, became very ill and often died after receiving a second injection some days later. Theobald Smith communicated his results verbally to Ehrlich, and later, Otto²in Ehrlich’s laboratory investigated more fully what he described as the “Theobald Smith phenomenon”. He was able to show that it was not confined to mixtures of diphtheria toxin and antitoxin and readily invoked by a foreign protein like horse serum. Subsequent work has clearly defined the conditions which will lead to the development of the state of anaphylaxis or, as it is often called anaphylactic shock.

Anaphylactic shock in animals

To produce anaphylactic shock, the animal must previously have had experience of the antigenic protein. After the first administration of the protein, certain changes take place in the body which is then said to be sensitised to the particular protein concerned. It is necessary for sensitisation that the antigen molecules reach the body cells in an unaltered state. Sensitisation is thus most conveniently brought about by parenteral injection, although inhalation and even ingestion are often effective. In the last case much of the protein will be destroyed in the alimentary canal, but the mucous membrane is apparently permeable to some extent to unchanged protein³ and since incredibly small amounts of antigen will sensitise the guinea pig (e.g. 1 μg of egg albumin or 0·000001 ml. of horse serum),⁴ it is only necessary for small quantities such as these to escape digestion and penetrate the alimentary mucosa. The size of dose required for sensitisation depends on the species of animal. Very small doses are effective in guinea pigs, but larger doses are needed for rabbits and dogs. On the other hand, excessively large doses may delay sensitisation or even prevent its occurrence.

Anaphylactic shock occurs when a second injection of antigen is given after a certain period of time. This latent period varies with different species and with the degree of sensitisation. A period of at least a week is required for all species, and with some a period of three to four weeks is preferable. Once this period has elapsed the resultant sensitivity may persist for an almost indefinite period. Shock is only produced if antigen reaches the sensitised cells in a relatively high concentration. Doses larger than those required for sensitisation are usually required and often the required concentration in the tissues can only be achieved by administering the antigen intravenously.

Animal species also differ one from the other in the signs, symptoms and pathological lesions of anaphylactic shock. Whereas the blood pressure in the rabbit and guinea pig rises, at least initially, in the dog it falls progressively. The guinea pig dies of asphyxia with signs of acute respiratory distress; the rabbit dies of acute right sided heart failure; while the dog dies of circulatory failure following the segregation of much of its circulating blood in the hepatic portal circulation. Nevertheless it is now generally believed that the main manifestations of anaphylactic shock are due to two main effects—contraction of smooth muscle and increased capillary permeability.

In the guinea pig the main symptoms are attributable to an intense contraction of bronchial smooth muscle, which in that animal is particularly well developed throughout the lung. Within a few minutes of the intravenous administration of antigen to a sensitised animal, there are signs of severe respiratory difficulty. When bronchial muscle contracts it is expiration that becomes difficult; this is seen in human asthmatics. A guinea pig in anaphylactic shock develops a syndrome very similar to a human asthmatic attack.⁵It becomes extremely cyanosed and dies within ten minutes. The post mortem picture shows over-inflated lungs, occluded bronchioles and local haemorrhage in the lungs and also other tissues. There is a considerable accumulation of polymorphonuclear leucocytes in the lung capillaries.

In the dog the predominant signs of anaphylactic shock are different. Death never takes place in less than 1 to 2 hours unless the animal is exceptionally well sensitised and may not occur at all. The most prominent symptom is prostration and weakness due to a profound fall in systemic blood pressure (e.g. from 120 down to 30 mm. Hg). This startling fall in blood pressure is due to a segregation of a large proportion of the circulating blood in the liver and hepatic portal circulation. This is brought about by an intense spasm of the smooth muscle in the walls of the hepatic vein. Not only is the liver the main organ to show changes in a dog undergoing anaphylactic shock but it is apparently responsble for most or perhaps all of the pathology of shock. Exclusion of the liver by ligature will prevent the onset of shock.⁶

The rabbit also shows distinctive features in anaphylaxis. This species is difficult to sensitise. Death following a challenge dose of antigen is caused by acute right heart failure. The right side of the heart is enormously dilated as a result of an intense contraction of the pulmonary artery. It is not only the pulmonary artery which contracts, however. Sudden blanching of the ears due to constriction of peripheral arterioles is a noticable feature of anaphylaxis in this animal, and arterioradiograph studies have shown that general arterial contraction occurs throughout the body.⁷

In all three species, the blood becomes less coagulable. Leucopenia (decrease in number of circulating leucocytes) in the peripheral blood is apparent and due to the accumulation of leucocytes in the capillaries of the lungs. A fall in the number of circulating platelets is also observed. Platelets appear to be segregated with the leucocytes in the lungs. In the dog, they are also found in the liver.

The antigenicity of the sensitising agent, the identity or immunologically specific relationship between this and the time required for sensitisation all point to the involvement of antibody in the anaphylactic reaction. This is made quite conclusive by the finding that sensitisation can be transferred passively. The transference of sensitivity with serum transferred from one animal to another has been noted for some time. It has also been shown that the degree of sensitivity produced by the transferred serum is related to its content of antibody.⁸ It is thus clear that the production of anaphylactic shock requires two components, namely antigen and antibody, to be present in the body at the same time and must therefore, be presumed to depend upon some interaction between the two.

The manifestations of anaphylaxis which have just been described as those which occur when an animal is injected with antigen on two occasions. The first injection stimulates antibody production and is termed the sensitising dose. The second injection of antigen, which brings about anaphylactic shock, is termed the challenge dose. Since under these experimental conditions the animal reacts to the challenge dose of antigen with antibodies of its own manufacture the resultant reaction is called active anaphylaxis. When an unsensitised animal is injected with serum from an actively sensitised animal the antibodies which that serum contains will sensitise the tissues of the unsensitised recipient. When this animal is given a challenge dose of antigen the resultant reaction is described as passive anaphylaxis. The reactions of passive anaphylaxis can be localised by injecting antibodies into a restricted area. A common example where restricted areas of skin are sensitised by intradermal injections of antibody and then challenged with antigen is passive cutaneous anaphylaxis. The terminology of anaphylactic reactions and the techniques by which they are produced has recently been lucidly described by Davies.⁵³

Allergy in humans

Whilst anaphylactic shock in experimental animals is a highly artificial condition brought about by the injection of antigen into the circulation of a previously sensitised animal, there are, however, a number of natural diseases for which there is evidence for an underlying mechanism essentially similar to that responsible for anaphylactic shock. These diseases which have been studied almost exclusively in man are the allergic diseases. Although some authorities make a clear distinction between these various diseases, there is a tendency nowadays to divide them into two groups. The first group includes those forms of allergy in which antibody can readily be demonstrated in the patient’s serum,...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Foreword
• Chapter 1: The immunological basis of allergic disease
• Chapter 2: Anaphylactic shock in experimental animals
• Chapter 3: The connective tissue mast cells and blood eosinophils
• Chapter 4: Histamine
• Chapter 5: The slow reacting substance of anaphylaxis
• Chapter 6: Bradykinin
• Chapter 7: Serotonin
• Chapter 8: Anaphylaxis and intermediary metabolism
• Chapter 9: The therapeutic control of allergic disease
• References
• Index